Such a press membrane is known from GB 2,069,358 A for example. In addition to inset elements in the form of reinforcing fabrics, transmission disks in the form of perforated steel disks are described in that British specification. Said steel disks are substantially thinner than the thickness of the press membrane. If a pressure load of the membrane occurs in the zone of the supporting cams, a flow of the rubber-elastic material occurs on either side of the transmission disk, thus leading to shearing stresses due to the shearing stresses at the surface of the virtually non-extensible transmission disks and thus to a shearing off of the rubber-elastic material. This often leads to a breakdown of the press membrane into several layers, as a result of which the progressing destruction of the press membrane is introduced. p EP 0 440 205 A1 discloses an alternative press membrane in which the transmission disks consist of two at first mutually separated half-disks which are moved towards the press membrane from opposite sides and are mutually connected there in the mounting position with the help of screws. The permanent connection of the transmission disks with the rubber-elastic membrane material is to occur by way of clamping between the two mutually joined half-disks. A disadvantage of this known membrane design is that in the case of a tensile load on the membrane within the disk plane (as occurs for example in the case of a pressurization of the filter chamber or the press water chamber), there is the likelihood that the rubber material clamped between the half-disks will partly slip out and thus the strength of the connection of the transmission disk will be lost. There is also the likelihood of damage to the rubber membrane in the zone of the comparably sharp-edged circumferential edges of the half-disk(s) projecting over the membrane surface.
A further press membrane is known from DE 41 19 166 C2. In order to seal the intermediate space which is pressurized with a pressure media, the pressure membrane engages with a circumferential shoulder in a circumferential groove which is adjusted thereto and is disposed in the frame of the filter plate. In the zone of the supporting cams of the filter plate the wall thickness of the press membrane is doubled in comparison with the other zones, with a fabric reinforcement being disposed in said enlarged zones within the rubber-elastic material. This fabric reinforcement is to be used to prevent deformations as will occur under such a high pressure load of the membrane in the zone of the supporting cams.
Since the rubber material as used for the press membrane principally concerns a substantially incompressible material, the high pressure load of the press membrane in the aforementioned zones leads to a virtual “flow” of the rubber material, whereas the fabric reinforcement is unable to follow such a flowing movement of the ambient rubber material. The consequence is a breakdown of the bond between the fabric reinforcement and the ambient rubber material, thus leading to a destruction of the press membrane in the form of fissuring in the rubber material at such places especially due to a multi-axial tension state.
Due to the flow movement of the rubber material there is a relative movement between the latter, the associated supporting cams of the filter plates and between the filter cloths disposed between the two aforementioned components. This leads to a high frictional wear on the rubber surface on the one hand and to an impermissibly large extension of the filter cloths on the other hand, which may result in the highly feared so-called cross-tears in the filter cloth fabric.
Another generally known press membrane is provided in the zone of the supporting cams with recesses, so that the supporting cams of opposite filter plates will rest on one another only via the two interposed filter cloths. Such a construction will not lead to any flowing of rubber material and fissuring in the same as well as to any overextension of the filter cloths caused by the flowing movement of the rubber material. A disadvantage of such a press membrane is that the membrane needs to be sealed in the zone of the recesses with respect to the filter plate in order to prevent any penetration of press water on the filtrate side. The measures required for such a reliable sealing are complex and will considerably drive up the price for a filter press based on such a principle.